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SYSLOG(3)		 BSD Library Functions Manual		     SYSLOG(3)

     syslog, syslog_r, vsyslog,	vsyslog_r, syslogp, syslogp_r, vsyslogp,
     vsyslogp_r, openlog, openlog_r, closelog, closelog_r, setlogmask,
     setlogmask_r -- control system log

     Standard C	Library	(libc, -lc)

     #include <syslog.h>

     syslog(int	priority, const	char *message, ...);

     syslog_r(int priority, struct syslog_data *data, const char *message,

     syslogp(int priority, const char *msgid, const char *sdfmt,
	 const char *message, ...);

     syslogp_r(int priority, struct syslog_data	*data, const char *msgid,
	 const char *sdfmt, const char *message, ...);

     openlog(const char	*ident,	int logopt, int	facility);

     openlog_r(const char *ident, int logopt, int facility,
	 struct	syslog_data *data);


     closelog_r(struct syslog_data *data);

     setlogmask(int maskpri);

     setlogmask_r(int maskpri, struct syslog_data *data);

     #include <stdarg.h>

     vsyslog(int priority, const char *message,	va_list	args);

     vsyslog_r(int priority, struct syslog_data	*data, const char *message,
	 va_list args);

     vsyslogp(int priority, const char *msgid, const char *sdfmt,
	 const char *message, va_list args);

     vsyslogp_r(int priority, struct syslog_data *data,	const char *msgid,
	 const char *sdfmt, const char *message, va_list args);

     The syslog() function writes message to the system	message	logger.	 The
     message is	then written to	the system console, log	files, logged-in
     users, or forwarded to other machines as appropriate (see syslogd(8)).

     The message is identical to a printf(3) format string, except that	`%m'
     is	replaced by the	current	error message.	(As denoted by the global
     variable errno; see strerror(3).)	A trailing newline is added if none is

     The syslog_r() function is	a multithread-safe version of the syslog()
     function.	It takes a pointer to a	syslog_data structure which is used to
     store information.	 This parameter	must be	initialized before syslog_r()
     is	called.	 The SYSLOG_DATA_INIT constant is used for this	purpose.  The
     syslog_data structure and the SYSLOG_DATA_INIT constant are defined as:

	   struct syslog_data {
		   int		   log_file;
		   int		   connected;
		   int		   opened;
		   int		   log_stat;
		   const char	  *log_tag;
		   int		   log_fac;
		   int		   log_mask;

	   #define SYSLOG_DATA_INIT { \
	       .log_file = -1, \
	       .log_fac	= LOG_USER, \
	       .log_mask = 0xff, \

     The structure is composed of the following	elements:

	   log_file   contains the file	descriptor of the file where the mes-
		      sage is logged

	   connected  indicates	if connect has been done

	   opened     indicates	if openlog_r() has been	called

	   log_stat   status bits, set by openlog_r()

	   log_tag    string to	tag the	entry with

	   log_fac    facility code

	   log_mask   mask of priorities to be logged

     The vsyslog() function is an alternative form in which the	arguments have
     already been captured using the variable-length argument facilities of

     The syslogp() variants take additional arguments which correspond to new
     fields in the syslog-protocol message format.  All	three arguments	are
     evaluated as printf(3) format strings and any of them can be NULL.	 This
     enables applications to use message IDs, structured data, and UTF-8 en-
     coded content in messages.

     The message is tagged with	priority.  Priorities are encoded as a
     facility and a level.  The	facility describes the part of the system gen-
     erating the message.  The level is	selected from the following ordered
     (high to low) list:

     LOG_EMERG	   A panic condition.  This is normally	broadcast to all

     LOG_ALERT	   A condition that should be corrected	immediately, such as a
		   corrupted system database.

     LOG_CRIT	   Critical conditions,	e.g., hard device errors.

     LOG_ERR	   Errors.

     LOG_WARNING   Warning messages.

     LOG_NOTICE	   Conditions that are not error conditions, but should	possi-
		   bly be handled specially.

     LOG_INFO	   Informational messages.

     LOG_DEBUG	   Messages that contain information normally of use only when
		   debugging a program.

     The vsyslog_r() is	used the same way as vsyslog() except that it takes an
     additional	pointer	to a syslog_data structure.  It	is a multithread-safe
     version of	the vsyslog() function described above.

     The openlog() function provides for more specialized processing of	the
     messages sent by syslog() and vsyslog().  The parameter ident is a	string
     that will be prepended to every message.  The logopt argument is a	bit
     field specifying logging options, which is	formed by OR'ing one or	more
     of	the following values:

     LOG_CONS	   If syslog() cannot pass the message to syslogd(8) it	will
		   attempt to write the	message	to the console

     LOG_NDELAY	   Open	the connection to syslogd(8) immediately.  Normally
		   the open is delayed until the first message is logged.
		   Useful for programs that need to manage the order in	which
		   file	descriptors are	allocated.

     LOG_PERROR	   Write the message to	standard error output as well to the
		   system log.

     LOG_PID	   Log the process id with each	message: useful	for identify-
		   ing instantiations of daemons.  (This PID is	placed within
		   brackets between the	ident and the message.)

     The facility parameter encodes a default facility to be assigned to all
     messages that do not have an explicit facility encoded:

     LOG_AUTH	   The authorization system: login(1), su(1), getty(8),	etc.

     LOG_AUTHPRIV  The same as LOG_AUTH, but logged to a file readable only by
		   selected individuals.

     LOG_CRON	   The cron daemon: cron(8).

     LOG_DAEMON	   System daemons, such	as routed(8), that are not provided
		   for explicitly by other facilities.

     LOG_FTP	   The file transfer protocol daemon: ftpd(8).

     LOG_KERN	   Messages generated by the kernel.  These cannot be gener-
		   ated	by any user processes.

     LOG_LPR	   The line printer spooling system: lpr(1), lpc(8), lpd(8),

     LOG_MAIL	   The mail system.

     LOG_NEWS	   The network news system.

     LOG_SYSLOG	   Messages generated internally by syslogd(8).

     LOG_USER	   Messages generated by random	user processes.	 This is the
		   default facility identifier if none is specified.

     LOG_UUCP	   The uucp system.

     LOG_LOCAL0	   Reserved for	local use.  Similarly for LOG_LOCAL1 through

     The openlog_r() function is the multithread-safe version of the openlog()
     function.	It takes an additional pointer to a syslog_data	structure.
     This function must	be used	in conjunction with the	other multithread-safe

     The closelog() function can be used to close the log file.

     The closelog_r() does the same thing as closelog(3) but in	a multithread-
     safe way and takes	an additional pointer to a syslog_data structure.

     The setlogmask() function sets the	log priority mask to maskpri and re-
     turns the previous	mask.  Calls to	syslog() with a	priority not set in
     maskpri are rejected.  The	mask for an individual priority	pri is calcu-
     lated by the macro	LOG_MASK(pri); the mask	for all	priorities up to and
     including toppri is given by the macro LOG_UPTO(toppri).  The default al-
     lows all priorities to be logged.

     The setlogmask_r()	function is the	multithread-safe version of
     setlogmask().  It takes an	additional pointer to a	syslog_data structure.

     The routines closelog(), closelog_r(), openlog(), openlog_r(), syslog(),
     syslog_r(), vsyslog(), vsyslog_r(), syslogp(), syslogp_r(), vsyslogp(),
     and vsyslogp_r() return no	value.

     The routines setlogmask() and setlogmask_r() always return	the previous
     log mask level.

	   syslog(LOG_ALERT, "who: internal error 23");

	   openlog("ftpd", LOG_PID | LOG_NDELAY, LOG_FTP);


	   syslog(LOG_INFO, "Connection	from host %d", CallingHost);

	   syslog(LOG_INFO|LOG_LOCAL2, "foobar error: %m");

	   syslogp(LOG_INFO|LOG_LOCAL2,	NULL, NULL, "foobar error: %m");

	   syslogp(LOG_INFO, "ID%d", "[meta language=\"en-US\"]",
		   "event: %s",	42, EventDescription);

     For the multithread-safe functions:

	   struct syslog_data sdata = SYSLOG_DATA_INIT;

	   syslog_r(LOG_INFO|LOG_LOCAL2, &sdata, "foobar error:	%m");

     logger(1),	syslogd(8)

     The BSD syslog Protocol, RFC, 3164, August	2001.

     The syslog	Protocol, Internet-Draft, draft-ietf-syslog-protocol-23,
     September 2007.

     These non-multithread-safe	functions appeared in 4.2BSD.  The multi-
     thread-safe functions appeared in OpenBSD 3.1 and then in NetBSD 4.0.
     The async-signal-safe functions appeared in NetBSD	4.0.  The syslog-pro-
     tocol functions appeared in NetBSD	5.0.

     It	is important never to pass a string with user-supplied data as a for-
     mat without using `%s'.  An attacker can put format specifiers in the
     string to mangle your stack, leading to a possible	security hole.	This
     holds true	even if	you have built the string "by hand" using a function
     like snprintf(), as the resulting string may still	contain	user-supplied
     conversion	specifiers for later interpolation by syslog().

     Always be sure to use the proper secure idiom:

	   syslog(priority, "%s", string);

     With syslogp() the	caller is responsible to use the right formatting for
     the message fields.  A msgid must only contain up to 32 ASCII characters.
     A sdfmt has strict	rules for paranthesis and character quoting.  If the
     msgfmt contains UTF-8 characters, then it has to start with a Byte	Order

BSD				  May 3, 2010				   BSD


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